1. Field of the Invention
The present invention concerns an electronic balance comprising a measuring transducer with a weighing pan and a signal processing module as well as an input unit and an output unit.
Factors that have an influence on the weighing results are the location where the balance is installed and the prevailing environmental conditions such as temperature fluctuations, vibrations, electrostatic fields, air drafts, etc., as well as the properties of the weighing samples themselves. Balances of more recent design are equipped with the capability to account for systematic measuring errors and to adjust the result values with a correction. An example of this is the automatic adjustment that takes place in a balance after the temperature has changed by a certain amount. Another example is the calibration of the balance at its actual location.
2. Description of the Related Art
From EP-B1 0424773, a precision balance is known in which the built-in and automatically activated calibration weight is applied and removed several times in succession for the purpose of determining the standard deviation. Each time, the measured value is registered and subsequently the standard deviation is calculated by the signal processing module and compared to a given reference value. If the calculated value is less than the reference value, then a new span calibration factor is calculated and stored in memory. On the other hand, if the calculated value is more than the reference value, the span calibration factor is not updated in memory, but the balance puts out a corresponding message. This known setup provides the capability to calibrate the balance and to determine the standard deviation, but only for the one load size of the calibration weight that is built into the balance. In addition, after an error message, it is necessary to check and restart the balance.
Even when known systematic measuring errors are taken into account, the result values are still subject to uncertainties due to systematic deviations that are known to exist but whose magnitude remains undetermined, such as a non-linearity that cannot be ascertained at all or not with sufficient accuracy, or due to random uncertainties as may be caused by, e.g., a momentary air draft or by the uncertainty in the value of a correction of a systematic measurement error. The user of a precise electronic balance will be familiar with the inevitable dispersion of the weighing results. From the specifications of a balance, one can conclude the general magnitude of the errors to be expected, but when making an actual measurement, the user will hardly get an idea of its accuracy, because the specific influence factors at the user's location have not been taken into account. However, the user's broader concern is to know the measurement uncertainty of the actual weighing results obtained at the actual location and under the actual conditions.